Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder. Engines have also been described using more than one injector to provide fuel to a single cylinder in an attempt to improve engine performance. Specifically, in US 2005/0155578 an engine is described using a port fuel injector and a direct injector in each cylinder of the engine.
Another approach utilizing multiple injection locations for different fuel types is described in the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. Specifically, the Heywood et al. papers describes directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle.
The inventors herein have recognized several issues with such systems. For example, it may be desirable to utilize two direct in-cylinder injectors for each cylinder in order to expand the operating range of certain combustion modes by enabling the delivery of different substances directly to the combustion chamber. However, in-cylinder direct injection systems can add significant cost and complexity to the engine system.
As one example, the above issues may be addressed by an engine system for a vehicle, comprising a combustion chamber; a first in-cylinder direct injector configured to deliver a first substance including at least gasoline directly to the combustion chamber at a first pressure; and a second in-cylinder direct injector configured to deliver a second substance including at least an alcohol directly to the combustion chamber at a second pressure less than the first pressure.
As another example, the above issues may be addressed by a method of operating an internal combustion engine including at least one combustion chamber, comprising: during each of a plurality of cycles of the combustion chamber: injecting a first substance including at least gasoline directly into the combustion chamber at a first pressure via a first in-cylinder direct injector; injecting a second substance including at least an alcohol directly into the combustion chamber at a second pressure less than the first pressure via a second in-cylinder direct injector; and initiating combustion of a mixture of air and the first and the second injected substances within the combustion chamber.
In this way, it is possible to provide different substances directly to the combustion chamber while also reducing the cost and complexity of one of the injection systems by instead utilizing a lower pressure injector for the delivery of a knock suppressing substance such as an alcohol. Further, engine knock may be reduced during spark ignition operation and auto-ignition timing may be controlled during the controlled auto-ignition operation by adjusting the amounts and/or timings of the delivery of two or more different substances via separate higher and lower pressure direct injections systems as will be described in greater detail herein.